Organic EL device and display

ABSTRACT

An organic EL device and display are provided. A red light emitting layer, a green light emitting layer, a blue light emitting layer are laminated in this order between an anode and a cathode, and an intermediate layer “a” formed by use of an organic material is provided between the green light emitting layer and the blue light emitting layer. The HOMO-LUMO energy gap in the intermediate layer “a” is greater than the HOMO-LUMO energy gap of a green light emitting material constituting the green light emitting layer. In addition, the intermediate layer “a” has a hole transporting property. In the case of configuring a display by use of the organic EL devices, color filters are provided on the light take-out surface side. This makes it possible to provide an organic EL device with which light emission components for three colors of red, green and blue with a good balance suited to use for a full-color display can be obtained at a high luminance.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Document Nos.P2003-298269 filed on Aug. 22, 2003 and P2004-019247 filed on Jan. 28,2004, the disclosures of which are herein incorporated by reference.

The present invention relates to an organic EL device in which anorganic layer including a light emitting layer is interposed between ananode and a cathode, and a display using the organic EL device.

In recent years, as a display to be used in place of a cathode ray tube(CRT), flat displays light in weight and low in power consumption havebeen an object of vigorous research and development. Among the flatdisplays, those displays which use self-light-emitting type displaydevices (so-called light emitting devices) such as organic EL(Electroluminescence) devices and organic EL devices have been paidattention to as a display capable of being driven with low powerconsumption.

Configurations for achieving a full-color display mode with the displayusing the light emitting devices as above-mentioned include one in whichan organic EL device capable of emitting white light is combined withcolor filters which respectively transmit only light in the blue, greenor red wavelength region. In addition, as the organic EL device foremitting white light, one having a configuration in which a blue lightemitting layer, a green light emitting layer, and a red light emittinglayer are laminated in this order from the hole transport layer side andwhich has three wavelength light emission components has been disclosed(see Japanese Patent Laid-open No. Hei 10-3990 (see, particularly, FIG.1)).

However, the white light emitting organic EL device with theabove-mentioned configuration is insufficient in balance of respectiveluminous intensities in blue, green and red wavelength regions.Therefore, it has been impossible by use of such organic EL devices toobtain a display comparable in color reproduction performance with aCRT.

SUMMARY

Accordingly, it is an object of the present invention to provide anorganic EL device having light emission components of three colors ofred, green and blue in a good balance suited to use for a full-colordisplay, having a high efficiency and being capable of stable lightemission for a long time, and a display excellent in color reproductionperformance and capable of being driven for a long time.

According to an embodiment of the present invention, there is providedan organic EL device including a plurality of light emitting layersdifferent in emission color and laminated between an anode and acathode, wherein an intermediate layer including an organic material isprovided at least one location between the light emitting layers.

In the organic EL device configured as above, with the intermediatelayer provided between the light emitting layers, it is ensured that theenergy of excitons generated by re-coupling of electric charges in eachlight emitting layer is less liable to be transferred between the lightemitting layers. Therefore, a lowering in luminous efficacy of aspecified light emitting layer due to the transfer of the energy of theexcitons is prevented from occurring. Accordingly, the balance betweenthe luminous efficacies of the respective color light emitting layers ismaintained.

Particularly, the energy of the excitons as above-mentioned is liable tobe transferred into a layer in which a material with a small HOMO(Highest Occupied Molecular Orbital)-LUMO (Lowest Unoccupied MolecularOrbital) energy gap is present, with the result of a lowering in theluminous efficacy of a light emitting layer which has a great HOMO-LUMOenergy gap. In view of this, it is preferable that the HOMO-LUMO energygap in the intermediate layer provided between the light emitting layersis set to be greater than the HOMO-LUMO energy gaps of the materialsconstituting the light emitting layers adjacent to the intermediatelayer. This configuration ensures that the transfer of theabove-mentioned energy between the light emitting layers is securelyprevented from occurring. In addition, the energy is prevented frombeing transferred into the intermediate layer to be released in theintermediate layer. Incidentally, the HOMO-LUMO energy gap in theintermediate layer may not necessarily be greater than the HOMO-LUMOenergy gaps of all the materials constituting the light emitting layersadjacent to the intermediate layer; in the case where there is amaterial having a HOMO-LUMO energy gap so small as to permit easytransfer of the energy of the excitons, it suffices that the HOMO-LUMOenergy gap in the intermediate layer is greater than the HOMO-LUMOenergy gap of this material. It should be noted here, however, that ifthe HOMO-LUMO energy gap in the intermediate layer is greater than theHOMO-LUMO energy gaps of all the materials constituting the lightemitting layers adjacent to the intermediate layer, the above-mentionedenergy transfer between the light emitting layers is securely preventedfrom occurring.

Furthermore, in the organic EL device configured as above, electrons orholes are transported into each light emitting layer through the lightemitting layer adjacent thereto. Therefore, it is preferable for theintermediate layer provided between the light emitting layers to have anelectron transporting property or a hole transporting property. Thispromises easy transportation of electrons or holes into the lightemitting layers adjacent to the intermediate layer. Therefore, in thecase where the light emitting layer provided on the cathode side is weakin luminous intensity, provision of an intermediate layer having both ahole transporting property and an electron blocking property on theanode side of this light emitting layer makes it possible to increasethe amount of the holes transported into the light emitting layerprovided on the cathode side and to restrict the amount of the electronstransported into the light emitting layer provided on the anode side,whereby the probability of re-coupling between electrons and holes inthe light emitting layer under consideration can be increased, and theluminous intensity can be enhanced. On the other hand, in the case wherethe light emitting layer provided on the anode side is weak in luminousintensity, provision of an intermediate layer having both an electrontransporting property and a hole blocking property on the cathode sideof the light emitting layer makes it possible to increase the amount ofthe electrons transported into the light emitting layer provided on theanode side and to restrict the amount of the holes transported into thelight emitting layer provided on the cathode side, whereby theprobability of re-coupling between electrons and holes in the lightemitting layer under consideration can be increased, and the luminousintensity can be enhanced.

Furthermore, the light emitting layers may include a red light emittinglayer, a green light emitting layer, and a blue light emitting layerlaminated in this order from the anode side, whereby holes can besufficiently injected into the green light emitting layer and the bluelight emitting layer on the cathode side relative to the red lightemitting layer, while sufficiently securing the luminous efficacy in thered light emitting layer.

In this case, an intermediate layer having both a hole transportingproperty and an electron blocking property is provided between the greenlight emitting layer and the blue light emitting layer. This ensuresthat the injection of holes into the blue light emitting layer providedon the most cathode side can be promoted, and the injection of electronsinto the green light emitting layer can be restricted, so that a goodprobability of re-coupling between holes and electrons in the blue lightemitting layer is secured. This also provides a well-balanced whitelight emission. In this instance, it is preferable for the LUMO energylevel (energy value) in the intermediate layer to be higher than theLUMO energy level of an electron transporting component serving as ahost material in the green light emitting layer, for providing a barrieragainst the injection of electrons into the green light emitting layer.

In this case, further, an intermediate layer having both a holetransporting property and an electron blocking property may be providedbetween the red light emitting layer and the green light emitting layer.This ensures that the injection of holes into the blue light emittinglayer and the green light emitting layer which are provided on thecathode side relative to the intermediate layer is promoted, theinjection of electrons into the red light emitting layer can berestricted, and the probabilities of re-coupling between holes andelectrons in the blue light emitting layer and the green light emittinglayer are secured. This also provides a well-balanced white lightemission. In this instance, it is preferable for the LUMO energy levelin the intermediate layer to be higher than the LUMO energy level of anelectron transporting component in the red light emitting layer, forproviding a barrier against the injection of electrons into the redlight emitting layer 12. This configuration makes it possible torestrict the injection of electrons into the red light emitting layer.

Besides, according to the present invention, there is provided a displaywherein a color filter is provided on the light take-out surface side ofthe above-described organic EL device.

According to the display as above, by combining a plurality of theorganic EL devices excellent in balance between emission colors withcolor filters for the respective colors, it is possible to take out therays in the emission colors with a good balance.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a sectional diagram showing a configuration of an organic ELdevice according to an embodiment of the present invention.

FIG. 2 is a sectional diagram showing another configuration (Example 1)of the organic EL device according to an embodiment of the presentinvention.

FIG. 3 is a schematic diagram showing the energy level in the organic ELdevice according to the embodiment of the present invention.

FIG. 4 is a sectional diagram showing a further embodiment (Example 2)of the organic EL device according to an embodiment of the presentinvention.

FIG. 5 shows the emission spectrum of an organic EL device produced inExample 1.

FIG. 6 is a schematic diagram showing the energy level in an organicfilm in Example 2.

FIG. 7 shows the emission spectrum of an organic EL device produced inExample 2.

FIG. 8 shows the emission spectrum of an organic EL device manufacturedin Comparative Example.

DETAILED DESCRIPTION

Now, the configuration of an organic EL device according to the presentinvention will be described in detail below based on the drawings. FIGS.1 and 2 are sectional diagrams schematically showing the organic ELdevices of the present invention.

Each of the organic EL devices 1 and 1′ shown in these drawings isprovided, for example, in each pixel of a substrate 2 constituting adisplay, includes an anode 3, an organic layer 4 and a cathode 5laminated in this order from the side of the substrate 2, and is coveredgas-tight with a protective film 6. Particularly, the organic EL device1 shown in FIG. 1 is configured to be of the so-called top emissiontype, in which the light h emitted by the organic EL device 1 is takenout on the side opposite to the substrate 2. On the other hand, theorganic EL device 1′ shown in FIG. 2 is configured to be of theso-called bottom emission type, in which the light h emitted by theorganic EL device 1′ is taken out on the side of the substrate 2.

Next, detailed configurations of the component parts of each of theorganic EL devices 1 and 1′ will be described in the order of thesubstrate 2, the anode 3, the cathode 5 paired with the anode 3, and theorganic layer 4 sandwiched between the anode 3 and the cathode 5.

<Substrate>

First, the substrate 2 is composed of a glass substrate, a siliconsubstrate, a plastic substrate, or a TFT (thin film transistor)substrate provided with a TFT, or the like; particularly, in the case ofthe bottom emission type organic EL device shown in FIG. 2, thesubstrate 2 is composed of a light transmitting material. In addition,where the organic EL device 1, 1′ is used in combination with otherdisplay device, the substrate may be used in common for both thedevices.

<Anode>

The anode 3 provided on the substrate 2 is composed of a conductivematerial having a great work function. Examples of the conductivematerial having a great work function include nickel, silver, gold,platinum, palladium, selenium, rhodium, ruthenium, iridium, rhenium,tungsten, molybdenum, chromium, tantalum, niobium, alloys of thesemetals, tin oxide (SnO₂), indium tin oxide (ITO), zinc oxide, andtitanium oxide.

<Cathode>

On the other hand, the cathode 5 connected to the anode 3 through apower supply 8 is composed of a conductive material having a small workfunction. Examples of the conductive material having a small workfunction include alloys of an active metal such as Li, Mg, Ca, etc. withsuch a metal as Ag, Al, In, etc., and laminates of these alloys. Inaddition, a structure may be adopted in which a layer of a compound ofan active metal such as Li, Mg, Ca, etc. with a halogen such asfluorine, bromine, etc. or oxygen or the like is inserted in a thin formbetween the cathode 5 and the organic layer 4.

Of the anode 3 and the cathode 5 as above, the one electrode disposed onthe side of taking up the emitted light h generated in the organic layer4 is composed by appropriately selecting and using a light transmittingone of the above-mentioned materials, and the thickness thereof is soregulated as to obtain a light transmittance suited to the use. On theother hand, the other electrode is composed by appropriately selectingand using a material having a good reflectance.

In addition, the anode 3 and the cathode 5 are patterned into a suitableshape depending on the drive system of the display to be constituted byuse of the organic EL devices 1 or 1′. For example, in the case wherethe drive system of the display is the simple matrix type, the anode 3and the cathode 5 are formed in the form of stripes intersecting eachother, and the intersection portions constitute the organic EL devices1, 1′. In the case where the drive system of the display is the activematrix type having a TFT for each pixel, the anode 3 is patternedaccording to each of a plurality of pixels arranged, in the state ofbeing connected to the TFT similarly provided for each pixel through acontact hole (not shown) formed in a layer insulation film covering theTFTs. On the other hand, the cathode 5 may be formed in the form of asolid film formed to cover the entire surface of the substrate 2, to beused as a common electrode for the pixels. It should be noted here thatin the case of adopting the active matrix type as the drive system ofthe display, it is preferable to use the top emission type organic ELdevice 1 shown in FIG. 1, since it is thereby possible to enhance thenumerical aperture of the device.

<Organic layer>

The organic layer 4 sandwiched between the anode 3 and the cathode 5includes a hole transport layer 10, a red light emitting layer 11, agreen light emitting layer 12, a blue light emitting layer 13, and anelectron transport layer 14 laminated in this order from the side of theanode 3. Particularly, the organic layer 4 is characterized in that theintermediate layer “a” is provided between the green light emittinglayer 12 and the blue light emitting layer 13. Now, the configurationsof the layers 10-15 and the intermediate layer “a” will be described inthis order.

<Hole Transport Layer>

First, the hole transport layer 10 provided on the anode 3 is a layerdesigned to transport the holes (positive holes). The hole transportlayer 10 may be composed by laminating a plurality of hole transportingmaterials, for enhancing the hole transport performance.

Examples of the material (hole transporting material) for forming thehole transport layer 10 include heterocyclic conjugated monomers,oligomers and polymers, including not only benzidine and derivativesthereof, styrylamine and derivatives thereof, and triphenylmethane andderivatives thereof but also porphyrin and derivatives thereof, triazoleand derivatives thereof, imidazole and derivatives thereof, oxadiazoleand derivatives thereof, polyarylalkanes and derivatives thereof,phenylenediamine and derivatives thereof, arylamines and derivativesthereof, oxazole and derivatives thereof, anthracene and derivativesthereof, fluorenone and derivatives thereof, hydrazine and derivativesthereof, stilbene and derivatives thereof, phthanocyanine andderivatives thereof, polysilane based compounds, vinylcarbazole basedcompounds, thiophene based compounds, aniline based compounds, etc.

Specific, but not limitative, examples of the hole transport materialsinclude α-naphthylphenyldiamine (α-NPD), porphyrin,metallotetraphenylporphrin, metallonaphthalocyanine,4,4′,4″-trimethyltriphenylamine,4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA),N,N,N′,N′-tetrakis(p-tolyl)p-phenylenediamine,N,N,N′,N′-tetraphenyl-4,4′-diaminobiphenyl, N-phenylcarbazole,4-di-p-tolylaminostylbene, poly(paraphenylenevinylene),poly(thiophenevinylene), poly(2,2′-thienylpyrrole), etc.

<Red Light Emitting Layer>

In the next place, the red light emitting layer 11 provided on the holetransport layer 10 is preferably so designed that some of the holesinjected through the hole transport layer 10 are re-coupled in the redlight emitting layer 11 to give red light emission, and the rest of theholes not contributing to the light emission in the red light emittinglayer are transported into the green light emitting layer 12, forcontributing to green light emission and blue light emission.

Such a red light emitting layer 11 is configured by combining therequired materials appropriately selected from (a) a red light emittingmaterial (fluorescent or phosphorescent), (b) a hole transportingmaterial, (c) an electron transporting material and (d) a positive andnegative charge transporting material. Each of these materials is usedtogether with a single or a plurality of materials appropriatelyselected from among the following material categories, as required, forsecuring light emission performance and hole transport performance.

The material categories include cyclopentadiene derivatives,tetraphenylbutadiene derivatives, triphenylamine derivatives, oxadiazolederivatives, bathophenanthroline derivatives, pyrazoloquinolinederivatives, styrylbenzene derivatives, styrylarylene derivatives,aminostyryl derivatives, silole derivatives, thiophene ring derivatives,pyridine ring compounds, perinone derivatives, perylene derivatives,oligothiophene derivatives, cumarin derivatives, rubrene derivatives,quinacridone derivatives, squalium derivatives, porphyrin derivatives,styryl based coloring matter, tetracene derivatives, pyrazolinederivatives, trifumanylamine derivatives, anthracene derivatives,diphenylanthracene derivatives, pyrene derivatives, carbazolederivatives, oxadiazole dimer, pyrazoline dimer, aluminum-quinolinolcomplex, benzoquinolinol-beryllium complex, benzoxazole-zinc complex,benzothiazole-zinc complex, azomethyl-zinc complex, porphyrin-zinccomplex, europium complexes, iridium complexes, platinum complexes, etc.and metal complexes having such a metal as Al, Zn, Be, Pt, Ir, Tb, Eu,Dy, etc. as a center metal and having an oxadiazole, thiadiazole,phenylpyridine, phenylbenzoimidazole or quinoline structure or the likeas a ligand.

Particularly, specific examples of (a) red light emitting materialinclude bis(aminostyryl)naphthalene (BSN) represented by the followingformula (1), which is a styrylarylene derivative. Such a styrylarylenebased material, examples of which are described in Japanese PatentLaid-open No. 2002-226722, can be used to dope a host material therewithin a high concentration, and has a hole transporting property due to itstriphenylamine skeleton. Therefore, when such a red light emittingmaterial is used, efficient red light emission and a high holetransporting property can be obtained, which is the reason why it ispreferable to form the red light emitting layer 11 in contact with thehole transport layer 10.

Specific, but not limitative, examples of (b) hole transporting materialinclude α-NPD, and specific, but not limitative, examples of (c)electron transporting material include4,4′-bis(2,2-dphenyl-ethen-1-yl)-diphenyl (DPVBi) represented by thefollowing formula (2), which is a styrylarylene derivative.

<Green Light Emitting Layer>

The green light emitting layer 12 provided on the red light emittinglayer 11 preferably has a positive and negative charge transportingproperty for transporting both holes and electrons. This characteristicproperty ensures that some of the holes injected through the red lightemitting layer 11 contribute to light emission in the green lightemitting layer 12, whereas the rest of the holes are transported intothe blue light emitting layer 13, and that some of the electronsinjected from the side of the blue light emitting layer 13 contribute tolight emission in the green light emitting layer 12, whereas the rest ofthe electrons are transported into the red light emitting layer 11. Thismakes it possible to achieve respective light emissions from the red,green and blue light emitting layers 11, 12, 13.

As a method for providing the green light emitting layer 12 with thepositive and negative charge transporting property, there may becontemplated the methods of (1) doping a positive and negative chargetransporting host with a green light emitting material, (2) doping ahole transporting host with an electron transporting green lightemitting material, (3) doping an electron transporting host with a holetransporting green light emitting material, (4) doping a mixed hostcomposed of a hole transporting material and an electron transportingmaterial with a green light emitting material, and so on. In thisinstance, the hole transporting material in the green light emittinglayer 12 may be the hole transporting material used to form the holetransport layer. In addition, the electron transporting material in thegreen light emitting layer 12 may be the electron transporting hostmaterial constituting the blue light emitting layer 13 which will bedescribed below.

As the material(s) for constituting the green light emitting layer 12, asingle material or a plurality of materials are appropriately selectedfrom among the above-mentioned material categories.

Furthermore, in the organic EL device 1 according to the presentinvention in which the red light emitting layer 11 is present on theside of the hole transport layer 10, the green light emitting layer 12is preferably provided between the red light emitting layer 11 and theblue light emitting layer 13. This is because of the problems that (1)in the case where the red light emitting layer 11 and the blue lightemitting layer 13 are adjacent to each other, the energy of the excitonsgenerated in the blue light emitting layer 13 would easily move into thered light emitting layer 11. As a result, a sufficient blue lightintensity would not easily be obtained, and that (2) in the case wherethe blue light emitting layer 13 is provided between the red lightemitting layer 11 and the green light emitting layer 12, the energy ofthe excitons would be deprived by both the red light emitting layer 11and the green light emitting layer 12, and the like problems. Besides,in the case of the configuration in which, for example, an electrontransporting host is doped with a hole transporting green light emittingmaterial, each of the layers constituting the organic layer 4 can beformed by binary co-deposition, which promises a function as a whitedevice and eliminates the need for such a complicated manufacturingprocess as that for ternary co-deposition.

<Blue Light Emitting Layer>

In the next place, the blue light emitting layer 13 provided on thegreen light emitting layer 12 has an electron transporting property.This ensures that some of the electrons injected through the electrontransport layer 14 into the blue light emitting layer 13 contribute toblue light emission in the blue light emitting layer 13, whereas therest of the electrons are transported into the green light emittinglayer 12 and the red light emitting layer 11 to contribute to greenlight emission and red light emission.

The blue light emitting layer 12 is configured by combining the requiredmaterials appropriately selected from among (a) a blue light emittingmaterial (fluorescent or phosphorescent), (b) a hole transportingmaterial, (c) an electron transporting material, and (d) a positive andnegative charge transporting material. As each of these materials, asingle material or a plurality of materials are appropriately selectedfrom among the above-mentioned material categories, as required, so asto secure light emission performance and hole transport performance.

Particularly, specific examples of (a) blue light emitting materialinclude perylene, specific examples of (b) hole transporting materialinclude α-NPD, and specific examples of (c) include DPVBi of the aboveformula (2), which is a styrylarylene derivative, the examples being notlimitative.

In addition, the blue light emitting layer 13 may have a positive andnegative charge transporting blue light emitting layer and an electrontransporting blue light emitting layer laminated in this order from theside of the green light emitting layer 12. With the blue light emittinglayer 13 having such a laminate structure, holes can be efficientlytransported to the whole region inside the blue light emitting layer 13,which enables a highly efficient and stable light emission with a highcolor purity. As a method for providing the blue light emitting layer 13with the positive and negative charge transporting property, there maybe contemplated the methods of (1) doping a positive and negative chargetransporting host with a blue light emitting material, (2) doping a holetransporting host with an electron transporting blue light emittingmaterial, (3) doping an electron transporting host with a holetransporting blue light emitting material, (4) doping a mixed hostcomposed of a hole transporting material and an electron transportingmaterial with a blue light emitting material, and so on.

The blue light emitting layer 13 according to the present invention isso configured that the energy of excitons generated through re-couplingof positive and negative charges in the blue light emitting layer 13 ismade to contribute to the light emission in the blue light emittinglayer 13 while minimizing the movement of the energy into the red lightemitting layer 11 and the green light emitting layer 12. Therefore, itis preferable for the blue light emitting layer 13 to be provided on themost cathode 5 side.

<Electron Transport Layer>

In addition, the electron transport layer 14 provided between the bluelight emitting layer 13 and the cathode 5 is a layer so designed as totransport electrons. The electron transport layer 14 may be configuredby laminating a plurality of electron transport materials, for enhancingthe electron transport performance.

Non-limitative examples of the electron transporting material as aboveinclude 8-hydroxyquinoline aluminum (Alq3), 8-hydroxymethylquinolinealuminum, anthracene, naphthalene, phenanthrene, pyrene, chrysene,perylene, butadiene, cumarin, acridine, stilbene, and derivativesthereof.

<Intermediate Layer>

In the next place, the intermediate layer “a” provided between the greenlight emitting layer 12 and the blue light emitting layer 13 is composedof an organic material having a HOMO-LUMO energy gap greater than theHOMO-LUMO energy gaps of the materials constituting the green lightemitting layer 12 and the blue light emitting layer 13. Here, in orderto prevent the energy of excitons generated in the blue light emittinglayer 13 from being transferred into the green light emitting layer 12,the intermediate layer is composed of an organic material having aHOMO-LUMO energy gap greater than the HOMO-LUMO energy gap of the dopantwhich is a light emitting material in the green light emitting layer 12.

In addition, in the case where, in the light emissions in the lightemitting layers 11, 12 and 13, the luminous intensity in the green lightemitting layer 12 disposed on the anode 3 side of the intermediate layer“a” is strong whereas the luminous intensity in the blue light emittinglayer 13 disposed on the cathode 5 side of the intermediate layer a isweak, the intermediate layer “a” is formed by use of a material whichhas the above-mentioned energy gap characteristic and has both a holetransporting property and an electron blocking property. On the otherhand, in the case where the luminous intensities are contrary to theabove, the intermediate layer “a” is formed by use of a material whichhas the above-mentioned energy gap characteristic and has both anelectron transporting property and a hole blocking property.Incidentally, here, the intermediate layer “a” has both a holetransporting property and an electron blocking property.

The organic material constituting the intermediate layer “a” having suchcharacteristics is appropriately selected among the materials usable forthe hole transporting layer 10, the materials usable for the lightemitting layers 11-13, and the materials usable for the electrontransport layer 14. In this case, taking into account the energy gapcharacteristics of the materials constituting the light emitting layers12 and 13 disposed adjacent to the intermediate layer a, a material withwhich the above-mentioned characteristics can be obtained is selectedfor forming the intermediate layer a. Specific examples of the organicmaterials to be used for the organic EL device 1, 1′ in the presentembodiment include those materials which have a hole transportingproperty and a comparatively great HOMO-LUMO energy gap, such as TPD,α-NPD, CBP, etc.

Besides, the film thickness of the intermediate layer “a” is set in therange of 0.1-20 nm, preferably 0.5-10 nm. This permits the intermediatelayer “a” to display its functions sufficiently. If the film thicknessof the intermediate layer “a” is below this range, the effects ofprovision of the intermediate layer “a” which are to be described belowcannot be obtained satisfactorily. On the other hand, if the filmthickness of the intermediate layer “a” is above the range, suchproblems as a rise in the drive voltage due to the organic layer 4, alowering in the drive life, and an unsatisfactory control of the chargere-coupling regions would be generated.

Incidentally, the position where to dispose the intermediate layer “a”is not limited to the position between the green light emitting layer 12and the blue light emitting layer 13, and the intermediate layer “a” canbe provided at any position between the light emitting layers. In thepresent embodiment, the intermediate layer “a” is provided at at leastone of the position between he green light emitting layer 12 and theblue light emitting layer 13 and the position between the red lightemitting layer 11 and the green light emitting layer 12. In addition, inthe case where a further plurality of light emitting layers arelaminated, the intermediate layer “a” can be provided at each positionbetween the light emitting layers. It should be noted here, however,that the same characteristics as above-mentioned are provided, takinginto account the characteristics of the intermediate layer “a” providedat any position and the light emitting layers disposed adjacent to theintermediate layer a.

Besides, the organic layer 4 configured to have the above-describedlaminate structure can be formed by applying a known method, such asvacuum evaporation and spin coating, while using the organic materialssynthesized by known methods.

In the case of configuring a full-color display by combining the organicEL devices 1 or 1′ configured as above with color filters, respectivecolor filters for transmitting only the rays in the blue, green and redwavelength regions are provided on the light take-out surface side ofthe plurality of the organic EL devices 1 or 1′.

According to the organic EL device 1 or 1′ configured asabove-described, with the intermediate layer “a” provided between thegreen light emitting layer 12 and the blue light emitting layer 13, theenergy of excitons generated by re-coupling of electric charges in eachof the green light emitting layer 12 and the blue light emitting layer13 are not liable to be transferred between the green light emittinglayer 12 and the blue light emitting layer 13. With the organic EL deice1 or 1′ having such a laminate structure, there have been cases wherethe energy of the excitons generated in the blue light emitting layer 13having a great HOMO-LUMO energy gap would be transferred into the greenlight emitting layer 12, with the result of a lowering in the luminousintensity in the blue light emitting layer 13. In the presentembodiment, however, the HOMO-LUMO energy gap in the intermediate layer“a” is set to be greater than the HOMO-LUMO energy gap of the dopantwhich is a light emitting material in the green light emitting layer 12,whereby it is ensured that the energy of the excitions generated in theblue light emitting layer 13 is not liable to be transferred into thegreen light emitting layer 12, and the intensity of blue light emissionin the blue light emitting layer 13 can be kept high. In addition, theenergy is prevented from being released into the intermediate layer “a”to be transferred in the intermediate layer a.

Moreover, with the red light emitting layer 11 provided on the mostanode 3 side, the red light emitting layer 11 can be formed by use of ahole transporting red light emitting material capable of dopingtherewith in a high concentration so that holes will be easilytransferred into the green light emitting layer 12 and the blue lightemitting layer 13 which are disposed on the cathode 5 side relative tothe red light emitting layer 11.

In such a condition, particularly since the intermediate layer “a” inthe present embodiment has both a hole transporting property and anelectron blocking property, holes can be sufficiently transported intothe blue light emitting layer 13 provided on the cathode 5 side relativeto the intermediate layer a, and the injection of electrons into thegreen light emitting layer 12 can be restricted, so that the probabilityof re-coupling between electrons and holes in the blue light emittinglayer 13 can be enhanced. This also contributes to enhancement of theintensity of blue light emission. In this case, for providing a barrieragainst the injection of electrons into the green light emitting layer12, it is preferable that the LUMO energy level in the intermediatelayer “a” having the hole transporting property is higher than the LUMOenergy level of the electron transporting component serving as the hostmaterial of the green light emitting layer 12. Such a configuration isshown, in terms of energy level, in FIG. 3. In the case of theconfiguration in which the hole transporting layer 10, the red lightemitting layer 11, the green light emitting layer 12, the intermediatelayer a, the blue light emitting layer 13, and the electron transportinglayer 14 are laminated in this order from the anode 3 side between theanode 3 and the cathode 5, it is preferable that the LUMO energy level[namely, the value of Energy (eV)] in the intermediate layer “a” ishigher than the LUMO energy level [namely, the value of Energy (eV)] ofthe electron transporting component serving as the host material of thegreen light emitting layer. This configuration makes it possible torestrict the injection of electrons into the green light emitting layer12.

Therefore, in the light emitting layers 11, 12 and 13, the rays in therespective colors can be taken out with good balance and at highefficiency, the balance between the luminous intensities for therespective colors is good, and white light emission with a good luminousefficacy can be obtained.

Incidentally, in the embodiment as above-described, the case where theintermediate layer “a” is disposed between the green light emittinglayer 12 and the blue light emitting layer 13 has been described as anexample. However, as above-mentioned, it suffices that the intermediatelayer is provided at at least one of the position between the greenlight emitting layer 12 and the blue light emitting layer 13 and theposition between the red light emitting layer 11 and the green lightemitting layer 12; in any case, the intermediate layer provided at anyposition is configured to have the same characteristics asabove-described, taking into account the characteristics of the lightemitting layers disposed adjacent to the intermediate layer.

For example, in an organic EL device 1″ in which an intermediate layer“a” is provided also between the red light emitting layer 11 and thegreen light emitting layer 12 as shown in FIG. 4, the intermediate layer“a′” is formed by use of an organic material having a HOMO-LUMO energygap greater than the HOMO-LUMO energy gaps of the materials constitutingthe red light emitting layer 11 and the green light emitting layer 12.In a specific example, for preventing the energy of excitons generatedin the green light emitting layer 12 from being transferred into the redlight emitting layer 11, the intermediate layer “a′” is formed by use ofan organic material having a HOMO-LUMO energy gap greater than theHOMO-LUMO energy gap of the dopant which is a light emitting material inthe red light emitting layer 11.

In addition, like in the above-described embodiment, in the case wherethe luminous intensity in the red light emitting layer 11 disposed onthe anode 3 side of the intermediate layer “a′” disposed between the redlight emitting layer 11 and the green light emitting layer 12 is strongand the luminous intensity in the green light emitting layer 12 disposedon the cathode 5 side of the intermediate layer “a′” is weak, theintermediate layer “a′” is formed by use of a material which has theabove-mentioned energy gap characteristic and has both a holetransporting property and an electron blocking property. On the otherhand, in the case where the luminous intensities are contrary to theabove, the intermediate layer “a” is formed by use of a material whichhas the above-mentioned energy gap characteristic and has both anelectron transporting property and a hole blocking property.

In the organic EL device 1″ configured in this way, the provision of theintermediate layer “a′” between the red light emitting layer 11 and thegreen light emitting layer 12 ensures that the energy of excitonsgenerated by re-coupling of electric charges in each of the red lightemitting layer 11 and the green light emitting layer 12 is not liable tobe transferred between the red light emitting layer 11 and the greenlight emitting layer 12. Particularly where the intermediate layer “a′”has both a hole transporting property and an electron blocking property,holes can be sufficiently transported into the green light emittinglayer 12 and the blue light emitting layer 13 provided on the cathode 5side relative to the intermediate layer a′, the injection of electronsinto the red light emitting layer 11 can be restricted, and theprobabilities of re-coupling between electrons and holes in the greenlight emitting layer 12 and the blue light emitting layer 13 can beenhanced. In this case, for providing a barrier against the injection ofelectrons into the red light emitting layer 11, it is preferable thatthe LUMO energy level in the intermediate layer “a′” having the holetransporting property is higher than the LUMO energy level of theelectron transporting component in the red light emitting layer 11. Thismakes it possible to restrict the injection of electrons into the redlight emitting layer 11.

Therefore, like in the above-described embodiment, in the respectivelight emitting layers 11, 12 and 13, the rays in the respective colorscan be taken out with good balance and at high efficiency, the balancebetween the luminous intensities for the respective colors is good, andwhite light emission with a good luminous efficacy can be obtained.

Besides, in the embodiment as above-described, the configuration whereinthe red light emitting layer 11, the green light emitting layer 12, andthe blue light emitting layer 13 are laminated in this order from theside of the anode 3 has been described, but the present invention is notlimited to such a lamination order, and a reverse lamination order canalso be adopted. It should be noted here, however, that the electrontransporting property of each of the light emitting layers is alsochanged appropriately. Specifically, the blue light emitting layerprovided on the most anode 3 side has at least a hole transportingproperty, the green light emitting layer provided on the cathode 5 sideof the blue light emitting layer has a positive and negative chargetransporting property, and the red light emitting layer provided on themost cathode 5 side has at least an electron transporting property. Insuch a configuration, also, the characteristics of the intermediatelayer provided between the light emitting layers can be considered inthe same way as above-described, and the same effects as above can beobtained.

For example, when an intermediate layer having a great HOMO-LUMO energygap as above-mentioned is provided between the blue light emitting layeron the most anode 3 side and the green light emitting layer on thecathode 5 side thereof, the energy of excitons generated in each of theblue light emitting layer and the green light emitting layer can beprevented from being transferred between the light emitting layers.Besides, in such a configuration, when the intermediate layer has bothan electron transporting property and a hole blocking property, theprobability of re-coupling of electric charges in the blue lightemitting layer disposed on the anode 3 side can be enhanced. In thiscase, for providing a barrier against the injection of holes into thegreen light emitting layer 12, the HOMO energy level in the intermediatelayer is set to be lower than the HOMO energy level of the holetransporting component in the green light emitting layer 12, whereby theinjection of holes into the green light emitting layer 12 can berestricted.

On the other hand, when the intermediate layer has both a holetransporting property and an electron blocking property, it is possibleto enhance the probabilities of re-coupling between electric charges inthe green light emitting layer and the red light emitting layer whichare disposed on the cathode 5 side relative to the intermediate layer.

Furthermore, the present invention is not limited to the configurationwherein an anode 3 is provided on a substrate 2, and an organic layer 4and a cathode 5 are laminated on the anode 3; the invention isapplicable also to an organic EL device having a configuration wherein acathode is provided on a substrate 2, and an organic layer and an anodeare laminated in this order on the cathode. Incidentally, in this casealso, by appropriately selecting the materials and film thicknesses ofthe cathode and the anode, it is possible to obtain both of a topemission type configuration and a bottom emission type configuration,and to obtain the same effects as those of the above-described organicEL devices 1, 1′ and 1″.

EXAMPLES Example 1

In Example 1, the bottom emission type organic EL device 1′ describedreferring to FIG. 2 was manufactured as follows.

First, a cell for an organic EL device was produced in which a film ofITO (about 100 nm thick) as an anode 3 was formed on a substrate 2composed of a 30 mm×30 mm glass plate, and other region than a central 2mm×2 mm light emission region of the anode 3 was masked with aninsulation film (omitted in the figure) by use of a photosensitiveorganic insulation material. Next, a metallic mask having an opening wasdisposed on the upper side of and in proximity to the substrate 2 in thecondition where the opening was matched to the exposed portion of theanode 3 (ITO) to be each light emission region, and the followingorganic layers were sequentially formed by a vacuum evaporation methodunder a vacuum of 10⁻⁴ Pa or below.

First, as the hole transport layer 10, a film of m-MTDATA(4,4′,4″-tris(3-methylphenylphenylamino)-triphenylamine) represented bythe following formula (3) was formed in a thickness of 20 nm, and then afilm of α-NPD (α-naphthyldiamine)Bis[N-(1-nephthyl)-N-phenyl]benzidinerepresented by the following formula (4) was formed in a thickness of 20nm. The vapor deposition rate was set to 0.1 nm/sec.

Next, as the red light emitting layer 11, a co-deposition film composedof DPVBi of the following formula (5) as a host doped with 30% of BSN ofthe following formula (6) as a red light emitting material was formed ina thickness of 5 nm. The vapor deposition rate was set to 0.2 nm/sec.

Thereafter, as the green light emitting layer 12, a co-deposition filmcomposed of a mixture of DPVBi and α-NPD in a mixing ratio of 1:1 as ahost doped with 1% of cumarin 6 of the following formula (7) as a greenlight emitting material was formed in a thickness of 10 nm. The vapordeposition rate was set to 0.2 nm/sec.

Then, a film of α-NPD was formed in a thickness of 3 nm as anintermediate layer “a” having a hole transporting property. The vapordeposition rate was set to 0.1 nm/sec. Incidentally, α-NPD has aHOMO-LUMO energy gap greater than the energy gap of cumarin 6 which is agreen light emitting material in the green light emitting layer 12. Inaddition, the LUMO energy level in α-NPD is higher than the LUMO energylevel of DPVBi which is an electron transporting component in the greenlight emitting layer 12.

Further, as the blue light emitting layer 13, a co-deposition layercomposed of DPVBi as a host doped with 3% of4,4′-(Bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi) of thefollowing formula (8) as a blue light emitting material was formed in athickness of 30 nm. The vapor deposition rate was set to 0.2 nm/sec.

Then, as the electron transport layer 14, a film of Alq3 represented bythe following formula (9) was formed in a thickness of 20 nm. The vapordeposition rate was set to 0.2 nm/sec.

Next, as the cathode 5, a thin film of Mg and Ag with a co-depositionratio of 10:1 was formed in a thickness of 50 nm, and a film of Ag wasformed in a thickness of 150 nm. The vapor deposition rate was set to0.5 nm/sec.

The emission spectrum of the organic EL device in Example 1 manufacturedas above-described is shown in FIG. 5. As shown in the figure, it wasconfirmed that blue, green and red light emission components can beobtained from the organic EL device according to Example 1. In addition,light emission with a luminance of 1337 cd/m² and CIE chromaticity(0.319, 0.294) at a current density of 25 mA/cm² was obtained evenlyover the light emission surface.

Example 2

In Example 2, an organic EL device 1″ of the bottom emission typedescribed referring to FIG. 4 was manufactured. Incidentally, FIG. 6shows a schematic diagram of the energy level in an organic layer inExample 2.

In this case, the bottom emission type organic EL device 1″ wasmanufactured in the same manner as in manufacturing the organic ELdevice in Example 1 above, except that a step of forming an intermediatelayer “a′” between the red light emitting layer 11 and the green lightemitting layer 12 was added to the manufacturing procedure in Example 1.It should be noted here, however, that the intermediate layer “a”between the green light emitting layer 12 and the blue light emittinglayer 13 was formed in a film thickness of 2 nm (in Example 1, the filmthickness was 3 nm). Besides, a film of α-NPD was formed in a thicknessof 2 nm as the intermediate layer “a′” between the red light emittinglayer 11 and the green light emitting layer 12. The vapor depositionrate was set to 0.1 nm/sec. Incidentally, α-NPD constituting theintermediate layer “a′” has a HOMO-LUMO energy gap greater than theenergy gap of BSN which is a red light emitting material in the redlight emitting layer 11. In addition, the LUMO energy level of α-NPD ishigher than the LUMO energy level of BSN serving as an electrontransporting component in the red light emitting layer 11.

The emission spectrum of the organic EL device in Example 2 manufacturedas above is shown in FIG. 7. As shown in this figure, it was confirmedthat the blue, green and red light emission components can be obtainedfrom the organic EL device in Example 2. In addition, light emissionwith a luminance of 1706 cd/m² and CIE chromaticity (0.324, 0.362) at acurrent density of 25 mA/cm² was obtained evenly over the light emissionsurface.

Comparative Example

In Comparative Example, an organic EL device having a configurationobtained by omitting the intermediate layer “a” from the configurationof the organic EL device 1′ manufactured in Example 1 above wasmanufactured. The organic EL device was manufactured following the samemanufacturing procedure in the above-described example, except foromitting the step of forming the intermediate layer a.

The emission spectrum of the organic EL device in Comparative Examplemanufactured as above is shown in FIG. 8. As shown in this figure, itwas confirmed that the blue, green and red light emission components canbe obtained from the organic EL device in Comparative Example. Lightemission with a luminance of 1311 cd/m² and CIE chromaticity (0.392,0.390) at a current density of 25 mA/cm² was obtained.

However, from a comparison of the emission spectra (Examples 1 and 2) inFIGS. 5 and 7 with the emission spectrum (Comparative Example) in FIG.8, it was confirmed that light emission with a greater blue lightemission component and a better balance of white light emission can beobtained with an organic EL device in which the intermediate layer isprovided according to Example.

INDUSTRIAL APPLICABILITY

As has been described above, according to the organic EL device of thepresent invention, rays in different wavelength regions can be emittedwith a good balance and at a high efficiency. Therefore, by laminatingthe light emitting layers for blue, green and red emission colors, it ispossible to achieve white light emission with a good balance of luminousintensities and a good luminous efficacy. In addition, according to thedisplay obtained by combining the organic EL devices with color filters,rays in the emission colors can be taken out in a good balance, and itis possible to configure a panel such that display with excellent colorreproduction characteristics can be achieved.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. An organic EL device comprising: a plurality of light emitting layersincluding a red light emitting layer, a green light emitting layer, anda blue light emitting layer laminated between an anode and a cathode; anelectron transport layer formed in contact with the cathode; and anintermediate layer comprised of an organic material provided in at leastone location between the light emitting layers, said intermediate layerhaving an electron blocking property and a hole transporting property,wherein the green light emitting layer comprises a hole transportingmaterial and an electron transporting material, and wherein the redlight emitting layer is formed in contact with a hole transporting layerthat is formed on the anode, and wherein an intermediate layercomposition of the intermediate layer is different than an electrontransport composition of the electron transport layer and different thana hole transporting composition of the hole transporting layer.
 2. Theorganic EL device as set forth in claim 1, wherein a HOMO-LUMO energygap of the intermediate layer is greater than a HOMO-LUMO energy gap ofat least one material constituting the light emitting layers disposedadjacent to the intermediate layer.
 3. The organic EL device as setforth in claim 2, wherein the HOMO-LUMO energy gap of the intermediatelayer is greater than a HOMO-LUMO energy gap of all of the materialsconstituting the light emitting layers disposed adjacent to theintermediate layer.
 4. The organic EL device as set forth in claim 1,wherein the intermediate layer is provided at least between the greenlight emitting layer and the blue light emitting layer, therebyrestricting the injection of electrons into the green light emittinglayer and promoting the injection of holes into the blue light emittinglayer.
 5. The organic EL device as set forth in claim 4, wherein a LUMOenergy level of the intermediate layer having a hole transportingproperty is higher than a LUMO energy level of an electron transportingcomponent in the green light emitting layer.
 6. The organic EL device asset forth in claim 1, wherein the intermediate layer is provided atleast between the red light emitting layer and the green light emittinglayer, thereby restricting the injection of electrons into the red lightemitting layer and promoting the injection of holes into the green lightemitting layer.
 7. The organic EL device as set forth in claim 6,wherein a LUMO energy level of the intermediate layer having a holetransporting property is higher than the LUMO energy level of anelectron transporting component in the red light emitting layer.
 8. Theorganic EL device as set forth in claim 6, wherein the organic materialfor the intermediate layer includes at least one of TPD and CBP.
 9. Theorganic EL device as set forth in claim 1, wherein the green lightemitting layer is formed directly on the red light emitting layer.
 10. Adisplay comprising: a color filter on a light take-out surface side ofan organic EL device comprising: a plurality of light emitting layersincluding a red light emitting layer, a green light emitting layer, anda blue light emitting layer laminated between an anode and a cathode; anelectron transport layer formed in contact with the cathode; and anintermediate layer provided in at least one location between the lightemitting layers, said intermediate layer having an electron blockingproperty and a hole transporting property thereby restricting theinjection of electrons into the green light emitting layer and promotingthe injection of holes into the blue light emitting layer, wherein thegreen light emitting layer comprises a hole transporting material and anelectron transporting material, and wherein the red light emitting layeris formed in contact with a hole transporting layer that is formed onthe anode, and wherein an intermediate layer composition of theintermediate layer is different than an electron transport compositionof the electron transport layer and different than a hole transportingcomposition of the hole transporting layer.
 11. An organic EL devicecomprising: an anode; a hole transport layer formed on the anode; aplurality of light emitting layers including a red light emitting layer,a green light emitting layer, and a blue light emitting layer laminatedon the hole transport layer such that the red light emitting layer isformed in contact with the hole transport layer that is formed directlyon the anode; an electron transport layer formed on the blue lightemitting layer; a cathode formed on the electron transport layer; and anintermediate layer comprised of an organic material provided between theblue light emitting layer and the green light emitting layer, saidintermediate layer having an electron blocking property and a holetransporting property, thereby restricting the injection of electronsinto the green light emitting layer and promoting the injection of holesinto the blue light emitting layer, wherein the red light emitting layeris configured so that a portion of the holes injected through the holetransport layer are re-coupled in the red light emitting layer to givered light emission and a remainder of the holes are transported into thegreen light emitting layer, wherein the green light emitting layercomprises a hole transporting material and an electron transportingmaterial, such that some of the holes transferred from the red lightemitting layer are re-coupled in the green light emitting layer to givegreen light emission and the remainder of the holes are transported intothe blue light emitting layer, and such that some of the electronsinjected from the blue light emitting layer contribute to green lightemission and the remainder of the electrons are transported to the redlight emitting layer, and wherein an intermediate layer composition ofthe intermediate layer is different than an electron transportcomposition of the electron transport layer and different than a holetransporting composition of the hole transporting layer.
 12. An organicEL device comprising: a plurality of light emitting layers including ared light emitting layer, a green light emitting layer, and a blue lightemitting layer laminated between an anode and a cathode; an electrontransport layer formed in contact with the cathode; and an intermediatelayer comprised of an organic material provided in at least one locationbetween the light emitting layers, said intermediate layer having anelectron transporting property and a hole blocking property, wherein thegreen light emitting layer comprises a hole transporting material and anelectron transporting material, and wherein the red light emitting layeris formed in contact with a hole transporting layer that is formed onthe anode, and wherein an intermediate layer composition of theintermediate layer is different than an electron transport compositionof the electron transport layer and different than a hole transportingcomposition of the hole transporting layer.